Discarded partially discharged batteries can present a significant danger. Alkali metal batteries present a particular problem. Because the alkali metal such as lithium will burn when exposed to water, a partially discharged battery presents a significant concern.
In order to address this issue, many lithium batteries incorporate a circuit to completely discharge the battery. After the battery has discharged to the point where it is no longer useful, the complete discharge circuit is activated, totally consuming the lithium, thereby reducing or eliminating any fire hazard.
One such device is disclose in McCaleb U.S. Pat. No. 5,119,00. This patent discloses a one-time switch used to close a complete discharge circuit. It requires that a pointed object push a switch element into the battery casing, closing the one-time switch. The battery then completely discharges and can be safely disposed.
Sink et al U.S. Pat. No. 6,270,916 utilizes a different discharge circuit. Instead of a switch, it uses a spring clip which contacts a conductor, closing the circuit. In order to prevent discharge, an insulating strip is place between the clip and the conductor. When it is desired to discharge the battery, the strip is removed, the spring clip then makes contact with the conductor, and the battery discharges. This has the advantage of not requiring a separate device to close the switch.
If the spring clip is not properly biased, the proper contact will not be made. Further, if the insulator strip is improperly positioned, it can cause a premature discharge of the battery. Moisture can also cause the circuit to close.